Piezoelectric actuators are employed in a wide variety of technical fields to actuate control elements. In such applications the piezoelectric actuators have the significant advantage of making possible rapid actuation with high dynamics and a high force.
A piezoelectric actuator is constructed from a plurality of piezoelectric layers. The individual piezoelectric layers are each arranged between two metal electrodes. To actuate the piezoelectric actuator an electrical voltage is applied to the piezoelectric layers, leading to a lengthening of the individual piezoelectric layers and to a lengthening of the piezoelectric actuator as a whole. So that the piezoelectric layer has a piezoelectric effect after it has been manufactured, whereby the thickness of the piezoelectric changes on application of an electrical voltage, it is necessary to first polarize the piezoelectric layers.
To polarize the piezoelectric layers an electrical polarization field, i.e. an electrical voltage is applied, which produces a remanent polarization and an ordered distribution of the domains aligned into the piezoelectric layers in the field direction of the polarization field compared to the unpolarized initial state. After the polarization of the piezoelectric layers the piezoelectric layers are remanent, i.e. permanently lengthened in the direction of the applied polarization field. The remanent lengthening of the piezoelectric layers is tailored to the stress conditions during the use of the piezoelectric actuator in that the polarization is undertaken under compressive stress. This reduces settling effects of the piezoelectric layers, which occur after polarization. A corresponding generic method is known from the International Patent Application with the international publication number 99/31739.
For polarizing the piezoelectric actuator voltages which can be changed over time are used since this achieves an improved polarization. The length of the piezoelectric actuator changes during the polarization process in accordance with the voltage pulses applied. Since the piezoelectric actuator is tensioned between two holders to represent the compressive stress, the compressive stress exerted by the holders on the piezoelectric actuator is changed by the change in length of the piezoelectric actuator. This has a negative effect on the polarization process of the piezoelectric actuator.